Answer:
Heather = 18 messages
Brian = 25 messages
Austin = 54 messages
Step-by-step explanation:
We know that Heather, Brian, and Austin sent a total of 97 messages.
Assuming the number of messages sent by Brian as x, we can say that Heather sent x-7 messages (7 fewer messages than Brian) and Austin sent 3(x-7) messages (3 times as many as Heather).
[tex](x-7)+x+3(x-7)=97\\\\x-7+x+3x-21=97\\\\5x=97+21+7\\\\5x=125\\\\x=25[/tex]
So Brian sent (x) messages = 25 messages,
Heather sent (x-7) messages = 25 - 7 = 18 messages; and
Austin sent 3(x-7) messages = 3(25-7) = 54 messages
